The analysis of subpopulations of white blood cells (leukocytes) in blood or bone marrow is of particular interest for the evaluation of immune system disorders and immune system-related diseases, especially of allergic diseases. Granulocytes are a subpopulation of leukocytes and encompass neutrophils, eosinophils as well as basophils, which all differ in their staining characteristics and abundance in blood.
Neutrophils are the most abundant white blood cells in humans and account for approximately 70% of white blood cells, while basophils and eosinophils are much rarer, accounting for less than 1 percent and 1-6% of white blood cells, respectively.
Both basophils and eosinophils play important roles in Immunoglobulin E-mediated (IgE-mediated) immune responses including food allergies, severe asthma and responsiveness to environmental allergens. The basophil and/or eosinophil count often increases prior to the onset of symptoms and the activation state of basophils and eosinophils may correlate with the symptoms.
Allergies of diverse causes are on the rise particularly in developed countries as a consequence of heightened susceptibility towards aeroallergens, (heavy) metals, metal alloys, food allergens, xenobiotics, microbial allergens and more. The identification and quantitation of IgE antibodies is central in common tests to diagnose allergy; however, not all allergies are IgE-mediated.
Food allergy is a major public health problem that affects as many as 3-4% of adults and 6% of children in the United States. The incidence of allergic diseases and food allergies has increased 10-fold in developed countries in the last two decades. Currently used, first-line methods for identifying offending antigens are based on in-vivo as well as in-vitro allergen tests.
The in-vivo allergen testing is usually carried out as a skin test, which is typically uncomfortable for the patient, in particular for the pediatric patient, and often inconclusive. In-vitro allergen tests include radio-allergo sorbent test (RAST), immunoCAP and histamine liberation tests. These assays are blood-based, typically require several milliliters of blood and several days until the test results are available; in addition, none of these have proven reliable in terms of specificity and sensitivity.
If these first-line assays remain inconclusive, an in-vivo food challenge test is carried out in a double-blind, placebo-controlled fashion to determine the offending allergen. This test is not only difficult to administer, it is also very time-consuming and, most importantly, potentially highly dangerous since it can result in anaphylactic shock and even death, if treatment is not initiated quickly.
Taken together, the identification of an offending allergen is not always possible and not all allergies are IgE-mediated, rendering many common in-vitro and in-vivo tests inadequate for the specific and reliable determination of the causes of allergic reactions. Consequently, there is a great, currently unmet need for specific, sensitive, safe and rapid methods to determine a subject's susceptibility to possibly offending allergens of diverse origin.